1. Field of the Invention
The present invention relates to an apparatus for controlling the operations of a construction machine such as a bulldozer, a power shovel at a remote location.
2. Description of the Related Art
At a site where restoration work is carried out for the damage caused by disaster or a site where dangerous construction work is carried out, there often arises an occasion that operations of a construction machine such as a bulldozer are remotely controlled. In the remote control, two types of radio control signal are used. One is analog signal and the other is on/off type digital signal. A system using analog signals has a high operability. However, it is expensive, and moreover, signal transmission capacity is small in which a limited number of channels can be used each operable at a low speed. On the other hand, a system using digital signals is inexpensive and can use a large number of channels (approximately 20 channels). For these reasons, the digital signal system is often employed in the field of construction machines in which a various kinds of signals are transmitted.
The system using an on/off type radio control signal cannot transmit a signal whose value ranges between the neutral state and the full working state. For example, there is a conventional bulldozer of a type which performs turning movement by means of a steering clutch and a steering brake. In the conventional bulldozer, the turning movement is performed by an on/off command issued from the steering clutch side and an on/off command issued from the clutch side. Such conventional bulldozer cannot perform a fine control of the turning movement so that an operator often feels unpleasant shocks during operation due to the vibration of the body of the bulldozer and turning movement cannot be achieved as desired.
Further, for raising and lowering working tools such as a blade and a ripper, the same problems as mentioned above are likely to occur, especially at the start of the operation.